[Asymmetrical changes in electrical activity of Purkinje fibers and muscle cells after administration of BAY K 8644. A new model of cardiac arrhythmia].

The effects of calcium current agonist BAY K 8644 on transmembrane potential of guinea pig papillary muscle (PM) and sheep Purkinje fibers (PF) were studied. The action potentials (AP) and contractions (C) were recorded. C both of PM and PF increased (two-four times) in response to BAY K 8644 (0.5-5 microM) addition. The AP duration of PM increased slightly (20%) while PF AP duration increased progressively with the time even at low BAY K 8644 dose (0.5 microM). At 5th min, early afterdepolarizations (EAD) occurred. After 10 min drug application PF became inexcitable at high plateau level. TTX and ethmozin (1 microM) restored AP. Thus, changes in ionic currents balance in PF towards the increase in inward calcium current by BAY K 8644 resulted in additional steady state potential at plateau level. The latter might induce EAD and re-entry around functionally inexcitable PF. The similarity of mechanisms of arrhythmias induced by ischemia with the presented model is discussed.